There are magnetic disks as magnetic recording media installed in a hard disk drive apparatus (HDD apparatus). The magnetic disk is manufactured by depositing a NiP film on a metal substrate made of an aluminium-magnesium alloy or the like, or applying a magnetic layer and protective layer onto a glass substrate or ceramic substrate. Conventionally, as a substrate for the magnetic disk, aluminum alloy substrates have widely been used. In recent years, with reductions in size and thickness and high-density recording in the magnetic disk, glass substrates have been used which are more excellent in flatness of the surface and strength in the thin plate as compared with the aluminum alloy substrate (Japanese Laid-Open Patent Publication No. H09-27150).
In recent years, in the magnetic disk installed in the HDD apparatus, the storage capacity will further increase in the future, and it has been required to further increase the recording speed and readout speed of the information in the HDD apparatus. Then, to meet these requirements, it is required to rotate the magnetic disk at higher speed.
However, when the magnetic disk is rotated at high speed in the HDD apparatus, a heavy load is imposed on the magnetic disk, and high strength (impact resistance) is required for the magnetic disk. Further, in recent years, since the HDD apparatus has been used in portable apparatuses such as, for example, notebook PCs, cellular telephones and portable music players, the magnetic disk is required to have high impact resistance such that the disk is not broken when the portable apparatus is dropped. Thus, required are magnetic disks (substrates for the magnetic disk) meeting impact resistance higher than currently required impact resistance.